The subject application is related to commonly-assigned United States patent applications entitled xe2x80x9cAir Conditioning System and Tubing Apparatus to Prevent Heat Gain due to Engine Compartment Heatxe2x80x9d and xe2x80x9cMulti-Function Receiverxe2x80x9d which were both filed on the same day as the subject application.
The subject invention generally relates to a thermostatic expansion valve (TXV) for use in an air conditioning system of a motor vehicle. More specifically, the subject invention relates to a TXV that controls the flow of refrigerant to an evaporator and a compressor of the air conditioning system under conditions of normal and low refrigerant charge.
A thermostatic expansion valve (TXV) is known in the art. In fact, the TXV has been utilized to regulate, i.e., control, a flow of refrigerant in air conditioning systems for many years. As understood by those skilled in the art, in addition to the TXV, the air conditioning systems also include a refrigerant compressor, a condenser, a receiver, and an evaporator.
The refrigerant is in a vapor or gaseous phase as it exits the evaporator. To appropriately control the flow of refrigerant in the air conditioning system, the TXV senses a superheat of the refrigerant as the flow leaves the evaporator. If the superheat of the refrigerant is too high, then the TXV opens to increase the flow of refrigerant into the evaporator which, in turn, reduces the superheat. On the other hand, if the superheat of the refrigerant is too low, then the TXV closes to decrease the flow of refrigerant into the evaporator which, in turn, increases the superheat.
It is understood in the art that, when the air conditioning system has low refrigerant charge and the superheat of the refrigerant is too high, a problem occurs. The problem is that there is not enough refrigerant throughout the air conditioning system to flow into the evaporator to reduce the superheat of the refrigerant. The TXVs of the prior art are unable to remedy this problem. That is, the TXVs of the prior art are unable to appropriately control the flow of refrigerant throughout the air conditioning system when the air conditioning system has low refrigerant charge.
Although the conventional TXVs are fully-open when the superheat of the refrigerant is too high, the superheat of the refrigerant remains too high since there is not enough refrigerant throughout the air conditioning system to flow into and through the evaporator and reduce the superheat. Since the flow of refrigerant through the evaporator is reduced, the evaporator essentially xe2x80x98trapsxe2x80x99 the refrigerant that is necessary to flow to the compressor to appropriately lube the compressor. That is, as the flow of refrigerant through the evaporator is reduced, the evaporator tends to trap oil that is necessary for lubrication of the compressor. Without appropriate lubrication, the operating life, i.e., the durability, of the compressor is jeopardized. The excessive superheat of the smaller amounts of refrigerant that do flow through the evaporator and to the compressor also jeopardize the operating life of the compressor as the refrigerant, in this condition, cannot remove heat from the compressor, as is desired. This result is undesirable and increases wear of the compressor.
Due to the inadequacies of the prior art, including those described above, it is desirable to provide a TXV that is able to control the flow of refrigerant to the evaporator and to the compressor under both normal and low refrigerant charge such that the operating life of the compressor is not jeopardized.
A thermostatic expansion valve (TXV) for use in an air conditioning system is disclosed. The air conditioning system includes a refrigerant compressor, a condenser in fluid communication with an outlet of the compressor, a receiver in fluid communication with an outlet of the condenser, and an evaporator in fluid communication with an outlet of the receiver and with an inlet of the compressor. The TXV of the subject invention controls a flow of the refrigerant to the evaporator under conditions of normal refrigerant charge and controls the flow of the refrigerant to both the evaporator and the compressor under conditions of low refrigerant charge.
The TXV includes a valve body having first and second ends and an interior wall defining a fluid chamber between the first and second ends. The TXV also includes a liquid refrigerant inlet and first and second liquid refrigerant outlets.
The liquid refrigerant inlet is defined within the valve body and is in fluid communication with the fluid chamber such that the refrigerant can flow from the receiver through the liquid refrigerant inlet and into the fluid chamber. The first liquid refrigerant outlet is defined within the valve body and is in fluid communication with the fluid chamber such that the refrigerant can flow from the fluid chamber through the first liquid refrigerant outlet and to the evaporator during the conditions of normal and low refrigerant charge. The second liquid refrigerant outlet is defined within the valve body and is in fluid communication with the fluid chamber such that the refrigerant can flow from the fluid chamber through the second liquid refrigerant outlet and to the refrigerant compressor during the conditions of low refrigerant charge.
A needle is disposed in the fluid chamber. The needle is moveable within the fluid chamber to control the flow of the refrigerant into and out of the valve body during the conditions of normal and low refrigerant charge. Furthermore, a notch is defined within the needle. The notch extends between the liquid refrigerant inlet and the second liquid refrigerant outlet. As such, during the conditions of low refrigerant charge, an amount of the refrigerant that flows into the fluid chamber from the receiver can flow through the fluid chamber to the second liquid refrigerant outlet and to the refrigerant compressor without flowing through the evaporator. The notch essentially established a bypass for the refrigerant to bypass the evaporator and flow directly to the compressor. The amount of the refrigerant that flows directly to the compressor xe2x80x98assistsxe2x80x99 or xe2x80x98protectsxe2x80x99 the compressor by guaranteeing that the compressor is appropriately tubed by the refrigerant. Furthermore, adequate amounts of the refrigerant flow to the compressor such that any heat present in the compressor is removed and the compressor can be cooled. Overall, the operating life of the compressor is improved as a result of the TXV of the subject invention.
Accordingly, the subject invention provides a TXV that assists the compressor by controlling the flow of refrigerant to the compressor under conditions of low refrigerant charge thereby maintaining an acceptable operating life for the compressor.